could be the sensor on the diff.. Could be that the computer is having difficulties as well.. In the mean time I would up-plug that ABS computer as having malfunctioning ABS IMO is worse then no ABS at all..

Jonathan

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Blue Ridge Mercedes
Jonathan Hodgman
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Enthusiast Service, Restoration & Tuning.
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Specializing in all pre and post merger AMG's including Hammers and DOHC M117 engines.
Mercedes Repair Atlanta